As farmers continue to focus on the efficiency of their operations, interest in optimum seed and fertilizer rates has grown. This desire to optimize seed and fertilizer rates has driven technology to deliver seed, fertilizer, and other products at rates specific for the type and quality of the soil. Thus, as the soil potential changes, so does the optimum product rate. Development in this technology has focused on control systems for agricultural metering systems and on meter drive systems that can vary the rate independent of the speed of travel.
Currently, a wide variety of metering systems are available that meter products in a rotatable fashion. These systems can be broadly classified into two categories, namely singulating meters and volumetric meters. Singulating meters deliver a specific number of seeds per rotation, and typically have a removable seed disk that is associated with each seed type and/or seed size. There are usually a small number of seeds delivered per meter rotation, and a rate chart is often supplied to instruct the operator how to set the drive transmission for the appropriate type of seed. Volumetric meters typically have to be calibrated with each seed variety to remain accurate due to factors such as the seed density, size, and moisture level effecting the amount of seed metered per rotation.
Many of the metering devices were initially developed with a mechanical ground drive system which includes a ground engaging wheel and a drive train having one or more chains and sprockets. Although conventional mechanical ground drive systems are relatively simple to understand, they have a number of disadvantages. For many mechanical systems, it is difficult to change the meter rate and for the majority of these systems, it cannot be changed during field operation. Moreover, the rate change may include changing sprockets and realigning chains on more archaic equipment or utilizing a rate changing box on more advanced mechanical drive systems. Cost, complexity, and wear are other disadvantages of this conventional drive system.
Some mechanical metering systems have been updated with an electric actuator to enable the operator to adjust the rates on the go. Although this is a vast improvement over most conventional drive systems, the operator still has to manually drive the meters to calibrate the system and priming a stationary air system to reduce the lag time from the meter to the opener in field operation is not achievable. Some manufactures have added hydraulic motors in the mechanical circuit to improve calibration functionality with additional cost and complexity to the overall system.
Different varieties of variable meter drive systems have been developed. These systems can be broadly classified as pure electrical systems, electrohydraulic meter drive systems, and solenoid controlled hydraulic valve systems.
Pure electric meter drive systems have been developed but are not widely used because of the power demands and costs required to deliver electrical power to an aircart. These systems are often attractive with one or two meter drives, but become unrealistic when three or more drives are required.
Electrohydraulic meter drive systems are designed with electric motors that provide a speed input to a hydraulic torque amplifier. Because the drive torque is amplified by hydraulics, there is a smaller electrical demand control with an electric motor results in good response times to rate changes, however, with three or more drives, the electrical requirements are greater than can be supplied by a typical tractor, and alternate power generation is required. Although electrohydraulic drive systems successfully provide the functionality for calibration and priming without a ground speed input, the system is more costly than other systems.
Solenoid controlled hydraulic valve systems are typically designed with solenoid controlled proportional valves and hydraulic motors. Electronic signals are sent from a controller to the proportional/valve's solenoid. The solenoid varies the position of the proportional valve and thus the oil flow to the hydraulic motor. The meter drive hydraulic circuits are typically plumbed in parallel with a second load or on a separate circuit.
Flexi-coil released a limited number of Model 1330 Plus variable rate aircarts in 1998. This system was designed with hydraulic motors that are driven with a solenoid controlled proportional valve block. The drive motors were run parallel with the fan motor, and the variable drive meters were plumbed in series to conserve hydraulic oil flow. The load on the fan motor sets the hydraulic pressure available to the meter drive circuit; therefore, when the fan load is reduced or the meter drive motor's pressure increases above the fan requirement the meter performance fails. This system successfully provides the functionality for calibration and priming without ground speed input.
The variable rate drive circuit of the Flexicoil model 9000 planter shared a separate line from a tractor remote with the transport circuit, since the two circuits would never be utilized at the same time. In this design, a 50/50 flow divider was used to divide oil flow to two different variable rate drive circuits. The flow divider was used to ensure that a constant supply of oil would flow to first bank of motors when the second bank was shut-off. If the flow divider was not used, when the second load is shut off, oil would flow to the second circuit (lowest circuit pressure), starving the first operating circuit. The second load is not infinitely adjustable such as in the case of an aircart where the second load is a fan.
Morris Industries released a series of VRT aircarts in approximately 1999. These carts have a metering circuit in parallel with the aircarts fan circuit. The meter circuit relies on the system load of the fan to generate the hydraulic pressure to drive the meters. If the parallel load drops below the requirement for the meters problems develop with the drive system.
Other variable meter drive systems have been developed with either a ground driven or engine mounted hydraulic pump that delivers oil to a hydraulic motor at the metering mechanism. However, these systems require constant adjustment to maintain accurate meter rates due to the changing volumetric efficiency of the pumps and motors as oil temperature changes. A ground drive system does not address priming or calibration of the meter and will not produce a hydraulic flow when the air seeder is stationary. These systems are also often very cost prohibitive.
CaseIH and Concord released a variable rate drive circuit in 1998 for both Aircarts and Planters with similar designs. U.S. Pat. No. 6,070,538 relates to this development. In the case of the aircart, the meter roller motors were placed in parallel with air cart's fan motor. Each meter and the fan were restricted with an electronically controlled proportional valve. The oil flow to the system is required to continuously change as the speed of the meters or the fan changes. The highest load sets the system pressure. This system was designed for the power beyond port on the tractor auxiliary remotes, which is not readily available on older tractors.
Tyler Industries released a variable rate drive circuit for a fertilizer spreader truck in 1999. This system utilized a separate pump circuit for the metering circuit. The metering circuit speed is controlled with a proportional restrictor valve. The circuit allows a bypass flow to eliminate meter creep when the meters are turned off. This system in not cost-effective for an aircart.
U.S. Pat. No. 6,109,192 was issued to John Deere & Company in August 2000, for a method of adjusting a mechanical gearbox on the go. This system is an enhancement to mechanical systems; however, this system could not be electrically primed, or calibrated as the input to the gearbox was driven from the wheels of the aircart.
Bourgault applied for Canadian Patent No. 2,311,698 in June, 2000, for a method to power a mechanical meter drive box while stationary. This system included an additional hydraulic motor that was operated when the speed input from the aircart's wheel was not available.
U.S. Pat. No. 6,145,455 was issued to Case Corporation on Nov. 14, 2000. This patent details a metering system for a planter that consists of either a variable or a constant displacement pump driven by a ground wheel. A variable pump control was utilized to change the displacement of a variable displacement pump and, therefore, the speed of the motors it was driving. The patent also teaches motor control with a constant displacement wheel driven pump. Because the system pump was driven proportionally to ground speed, the control system would only have to adjust the system for volumetric efficiency changes. The pump could not be used to calibrate or prime the system when stationary because it is tied to ground speed. The system only concentrates on the meter circuit; a separate circuit is required to drive the planter's fan. This system is very costly due to the additional pump, associated components and the structures required to draw power from the ground wheel.
It is, therefore, desirable to provide a cost-effective hydraulic circuit for an air seeder that provides a constant and minimum flow of hydraulic fluid to the variable rate drive system before providing a flow of hydraulic fluid to any secondary devices.